In the last ten years, there has been a rapid growth of industry and residences into rural and isolated areas. Thus, more people are having to spend more time in what used to be rural and isolated areas. Since there are more people in these areas now, there is now a need for additional telephone support in these areas. For example, there is a need for pay phones throughout these areas to allow people to make telephone calls. Pay phones are phones in which a user pays for the call using money or credit cards and they are usually placed in public areas. The cellular pay phones are fixedly installed but are connected via radio signals to a cellular system, thus the term cellular pay phone. Debit phones are regular cellular phones with a prepaid number of call credits. Debit phones are typically used in markets where fraud or the occurrence of people not paying their bills is prevalent. Typically, pay phones are connected to land line systems by telephone cables. However, it can be very expensive to run new land line cables to isolated or rural areas which did not previously have land line telephone service. In addition, the cellular provider may want to provide pay phones in areas in which the cellular provider does not have a land line system. Furthermore, the cellular provider may want to provide cellular pay phones on public transportation vehicles such as trains or buses.
FIG. 1 illustrates a cellular communication system which can provide support for cellular pay phones and debit phones. FIG. 1 illustrates 10 cells, C1-C10, of a cellular radio system. For each cell, there is a corresponding base station B1-B10. Remote stations which can either be cellular pay phones, debit phones, or regular cellular phones are shown as M1-M10. Some of the remote stations may be moved within a cell and from one cell to another. A mobile switching center MSC is connected to all of the base stations by cables or other fixed means, like radio signals. The MSC is also connected by cables or links to a fixed public telephone network or a similar fixed communication network. The MSC communicates with the remote stations by sending signals or commands to the base stations wherein the base stations transmit and receive the appropriate signals to and from the remote stations.
One requirement for pay phone/debit phone service is that the pay phones/debit phones need to be given charge rate information, a currency unit per time unit, for each call so that the user will know how much money to deposit into the machine or how much money is going to be charged to a credit or debit card for the call or how many monetary units will be removed from the prepaid amount in the debit phone. Some analog AMPS (Advanced Mobile Phone Service system) operators have introduced pay phones into their cellular networks using Charge Rate Order messages (CRO) to send the charge rate information to the pay phone/debit phone. The Charge Rate Order is a standard function in the British TACS system which happens to also work in AMPS systems but only as a non-standardized proprietary function. In some systems, the Charge Rate Order is based upon giving the cellular phones a special subscriber category (MCH) which differentiates them from ordinary cellular subscriptions. When a call is made and the mobile switching center detects that the called party has answered the call, the MSC checks the MCH category of the originating phone. If the category indicates that the cellular phone is indeed a pay phone/debit phone, the CRO function within the MSC sends a message to the pay phone/debit phone through the appropriate base station indicating that the called party has answered the call and which charge rate is to be used during the call. However, there are several problems with using charge rate order functions. First of all, the charge rate order is a standard TACS function only and is not standardized in AMPS/D-AMPS systems. Furthermore, when authentication was introduced into AMPS/D-AMPS systems, a spare air interface order code was used for authentication which happens to be the same air interface order code as charge rate order. Thus, the charge rate order message can no longer be used to send the charge rates in AMPS/D-AMPS systems. Finally, charge rate order only worked with analog channels on AMPS systems, which is now a problem since some cellular systems now support both analog and digital channels.
In the Pan-European digital TDMA cellular system known as the Global System for Mobile Communications (GSM), a remote station is supplied with charge advice information (CAI) at the charging point on a per call basis, in a signalling message over the radio interface. The CAI service is provided in the GSM specification as an original/specific service. The remote station receives at the beginning of each call, and as necessary during the call, a message containing the charge advice information. The charge advice information contains a plurality of elements which define various parameters associated with calculating the cost of making the call. The remote station uses the CAI elements to compute an advice of charge (AOC) value for the relevant call.
As noted above, the AMPS/D-AMPS systems do not support charge rate orders. It is not practicable to introduce a specific dedicated message for this function in the AMPS/D-AMPS system for several reasons. First of all, it would require upgraded software not only in the mobile service centers and remote stations, but also in radio base stations. That is, to use a solution according to GSM, all old base stations where a pay phone is to be connected would have to be upgraded. Furthermore, a debit phone roaming into an area served by old, non-upgraded base stations, would not work. Furthermore, it takes time to standardize and implement new messages in the AMPS/D-AMPS system. Thus, there is a need for a solution where only the MSC software and the pay/debit phones need to be upgraded in order to provide appropriate cellular coverage.